feat: key-contacts

This change introduces a new type of contacts
identified by their public key fingerprint
rather than an e-mail address.

Encrypted chats now stay encrypted
and unencrypted chats stay unencrypted.
For example, 1:1 chats with key-contacts
are encrypted and 1:1 chats with address-contacts
are unencrypted.
Groups that have a group ID are encrypted
and can only contain key-contacts
while groups that don't have a group ID ("adhoc groups")
are unencrypted and can only contain address-contacts.

JSON-RPC API `reset_contact_encryption` is removed.
Python API `Contact.reset_encryption` is removed.
"Group tracking plugin" in legacy Python API was removed because it
relied on parsing email addresses from system messages with regexps.

Co-authored-by: Hocuri <hocuri@gmx.de>
Co-authored-by: iequidoo <dgreshilov@gmail.com>
Co-authored-by: B. Petersen <r10s@b44t.com>

python/src/deltachat/chat.py

@@ -417,7 +417,13 @@ class Chat:
         :raises ValueError: if contact could not be added
         :returns: None
         """
-        contact = self.account.create_contact(obj)
+        from .contact import Contact
+
+        if isinstance(obj, Contact):
+            contact = obj
+        else:
+            contact = self.account.create_contact(obj)
+
         ret = lib.dc_add_contact_to_chat(self.account._dc_context, self.id, contact.id)
         if ret != 1:
             raise ValueError(f"could not add contact {contact!r} to chat")